Communication systems and specifically satellite communication systems use orthogonal linear polarizations to increase the transmission capacity of the communications channel. Conventional systems which employ such polarizations require lengthy and restrictive line-up procedures to ensure that the transmit and receive polarizations are properly aligned. If the polarizations are not properly aligned, a significant amount of undesired power (or “bleed through”) may be introduced on the orthogonal polarization, which may cause severe interference to communication signals on the orthogonal polarization, affecting the quality of these signals. For this reason, various line-up procedures have been developed to correctly tune the polarization alignment. Typically, these alignment procedures try to line-up a transmitting antenna polarization with the satellite's receive antenna polarization as well as a ground receiving antenna with the satellite's transmit antenna polarization.
Polarization line-up procedures involve measuring the power difference between a signal with the co-polarization (which is the correct polarization) and that due to cross-polarization “bleed-through”. During this procedure, the polarization is adjusted until the power difference between the two polarizations is at a maximum. This difference is technically referred to as the “cross-polarization isolation”. A typically acceptable value for cross-polarization isolation is 30-35 dB.
Traditionally, polarization isolation measurements are made using a continuous wave (CW) signal, because this kind of signal can be transmitted with a very high power density. This high power density allows the direct measurement of the CW signal on the co- and cross-polarizations. This measurement technique has a limitation in that it requires that the carrier be taken out of service and placed into CW mode in order to determine the cross-polarization isolation.